1. Field of the Invention
The present invention relates to a luminescent composition containing fluorescent bodies, a light source device having the luminescent composition, a display device having the light source device, and a process for preparing a luminescent composition.
2. Description of the Related Art
In liquid-crystal displays and display devices such as a flat-panel display (FPD), since an optical element (e.g., liquid-crystal element) used for optical output is not a self-luminous but passive element that modulates light supplied from the outside, the display devices generally include a light source device utilized as a backlight in addition to the optical element.
Typically, there are two types of backlight, namely, a direct-light backlight and an edge-light backlight.
Such backlight usually include a cold cathode tube. However, a light-emitting diode (LED) with high luminous efficiency has recently been developed; and research has now been conducted on the use of the LEDs for a light source of the backlight.
An example of a known LED light source utilized as a backlight is a white LED having fluorescent bodies (yellow fluorescent bodies) for converting blue light into yellow light. The fluorescent bodies or yellow fluorescent bodies are dispersed around a blue LED to emit blue light, and synthesize the blue light with yellow light to produce white light. Japanese Unexamined Patent Publication No. H08-007614 also discloses a light source produced by dispersing yellow fluorescent bodies on a light guide plate, a reflecting sheet, an optical filter and the like, and irradiating the yellow fluorescent bodies with blue light using a blue LED from a distance.
However, according to such light sources where visible light regions are covered by yellow excluding a blue light region, it is difficult to obtain desired properties in the use of the light source to displays. In particular, it is difficult to obtain properties for producing respective colors of red (R), green (G), and blue (B). Properties herein imply chromaticity in brightness and the respective colors RGB.
In contrast, in the applications of displays, Japanese Unexamined Patent Publication No. 2004-327492 discloses a display device produced by selecting a fluorescent body (green fluorescent body) for converting blue light into green light or a fluorescent body (red fluorescent body) for converting blue light or green light into red light to obtain properties proximate to the desired properties.
However, in producing a light source using the fluorescent bodies, it is difficult to appropriately disperse the fluorescent bodies. If the size of a fluorescent body is large (e.g., secondary particle), a surface area of the fluorescent body per unit decreases so that light gathering efficiency of excitation light in blue light or luminous efficiency decreases.
As a result, in a light source device and a display device using fluorescent bodies, if a large amount of secondary particles are produced in a fluorescent body portion where fluorescent bodies are dispersed, properties may largely deteriorate.